Umbra

Description

"Umbra and Penumbra. A solar eclipse, with the penumbra, d, c, and the umbra or dark shadow is seen here. When the Moon is at its greatest distance from the Earth, its shadow m o, sometimes terminates, before it reaches the Earth, and then an observer standing directly under the point o, will see the outer edge of the Sun, forming a bright ring around the circumference of the Moon, thus forming an annular eclipse." —Comstock, 1850